import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
         socket = new DatagramSocket(port);
    }
    public void start() throws IOException {
        System.out.println("服务器启动");
        while (true){
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);//进行 receive 操作的关键就是,这里的参数构造 相当于一个空盘子
            socket.receive(requestPacket);
            String request = new String(requestPacket.getData(),0,requestPacket.getLength());//拿到整个 UDP 数据报(从0开始,一直到贯穿整个数据报长度)
            String response = this.process(request);//指向了子类实例,这里调用的是子类的 process

            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);

            System.out.printf("[%s:%d] req=%s resp=%s\n",requestPacket.getAddress(),requestPacket.getPort(),
                    request,response);
        }
    }

    public String process(String request){
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }
}
